a) Field of the Invention
This invention relates to a method for producing a slip casting mold to be used for the production of a hollow ceramic article for insert casting, which is used in an exhaust gas system of an internal combustion engine, and a method for producing a hollow ceramic article for insert casting by the use of the slip casting mold.
b) Related Art Statement
There has been known a method, wherein the an internal surface of an exhaust port or exhaust manifold, which constitutes the exhaust gas system of an internal combustion engine of an automobile, is lined with a hollow ceramic article, and the exhaust gas temperature is raised by the adiabatic effect of the ceramic article, whereby the purifying the action of a catalyst for purifying exhaust gas is enhanced. Such a hollow ceramic article is generally insert cast in a cast metal, such as aluminum or the like, concurrently with the production of a cylinder head and the like.
However, when such hollow ceramic article is insert cast in a cast metal, such as aluminum or the like, a high compression stress acts on the hollow ceramic article due to shrinkage of the melted metal, and the hollow ceramic article may be broken. In order to obviate these drawbacks, a method has been proposed, wherein the outside of a hollow ceramic article is wrapped with an elastic material to relax the compression stress formed in the article; a method wherein the strength of a hollow ceramic article itself is improved; and the like. However, a satisfactory result has not yet been obtained in a hollow ceramic article having an elliptic cross-sectional shape which has partly a concave shape. The reason is that an excess tensile stress is generated in the concave portion. Particularly, when a sliding phenomenon is caused between the ceramic article and a cast metal, the metal is peeled off from the ceramic article, and further the tensile stress is concentrated in the concave portion, and hence such a hollow ceramic article is apt to be easily broken.
As an effective means for preventing the sliding phenomenon between a ceramics article and a metal, the inventor has proposed in Japanese Patent Laid-open Application No. 1-241,368, a method for producing a hollow ceramics article by means of a slip or casting mold having an inner surface roughened by sandblasting. However, it has been discovered in an investigation carried out later that, although a hollow ceramic article produced through the molding of a ceramic by means of a slip casting mold, whose inner surface had been roughened by sandblasting, has improved adhesion with a metal, the hollow ceramic article is large in dimensional dispersion, and hence the article has a problem fitting with other members, and other problems.
The object of the present invention is to solve the above described problems and to provide a method which can greatly increase the surface roughness of a hollow ceramics article to increase the adhesion of the ceramic article with metal without increasing its dimensional dispersion, whereby the stress concentration in the hollow ceramic article can be relaxed.
The inventor has made various investigations in order to attain the above described object and discovered that the object can be attained by a method wherein a slip casting mold itself, which is used for the production of a hollow ceramic article, is not treated by sandblasting or the like, but a particular treatment is carried out in the production of a mold to be used for the production of the slip casting mold. In the specification, claims and abstract of this invention, the term "mold" is used as a general term for master model, a so-called master mold and case mold produced by transferring the master mold, as explained later. That is, the term "mold" may have a meaning of master model, master mold or case mold.